<template>
  <div class="music-list">
    <div class="back" @click="back" >
      <i class="icon-back"></i>
    </div>

    <h1 class="title" >{{title}}</h1>

    <div class="bg-image" :style="bgStyle" ref="bgImage">
      <div class="play-wrapper" v-show="songs.length" ref='play'>
        <div class="play" @click='random'>
          <div class="icon-play"></div>
          <div class="text">随机播放全部</div>
        </div>
      </div>
      <div class="filter" ref="filter"></div>
    </div>
    <div class="bg-layer" ref='layer'></div>
    <scroll :data="songs" 
             class="list" ref="list"
            :listenScroll='listenScroll'
            :probeType='probeType'
            @scroll="scroll"
    >
      <div class="song-list-wrapper">
        <song-list 
          :songs="songs"  
          @selectSong="selectSong"
          :rank='rank'
        ></song-list>
      </div>
      <loading class="loading-container" v-show="!songs.length"></loading>
    </scroll>
  </div>
</template>

<script>
import scroll from 'base/scroll/scroll'
import songList from 'base/song-list/song-list'
import loading from "base/loading/loading";
import { mapActions } from 'vuex'
//顶端滚动留白值
const SAVE_TOP=40

export default {
  methods:{
    scroll(pos){
      this.scrollY=pos.y
    },
    back(){
      this.$router.back()
    },
    selectSong(item,index) {
      this.selectPlay({
        list: this.songs,
        index
      })
    },
    ...mapActions([
      // 将 `this.selectPlay()` 映射为 `this.$store.dispatch('selectPlay')`
      'selectPlay',
      'randomPlay'
    ]),
    //点击随机播放按钮
    random() {
      this.randomPlay ({
        list: this.songs
      })
    }
  },
  watch:{
    scrollY(newY){

      //歌曲list 黑色背景跟随滚动
      // scrollHightY: layer最大滚动的高度
      let scrollHightY=Math.max(newY,this.minHeight)
      this.$refs.layer.style['transform']=`translate3d(0,${scrollHightY}px,0)`
      this.$refs.layer.style['webkitTransform']=`translate3d(0,${scrollHightY}px,0)`
     
      let zIndex=0
      let scale =1
      //图片放大比例
      const precent=Math.abs(newY /this.offHeight )
      if(newY>0){
        scale=1+precent
        //图片层级 提高放大区域效果
        zIndex=10
      }
      
      
      if(newY<scrollHightY){ //歌曲list滚出顶部时
        //给顶部导航留白
        zIndex=10
        this.$refs.bgImage.style.height=`${SAVE_TOP}px`

        //把播放按钮隐藏
        this.$refs.play.style.display='none' 
        this.$refs.bgImage.style.paddingTop=0
      }else{

        //bgImg和播放按钮复原 
        this.$refs.bgImage.style.paddingTop='70%'
        this.$refs.bgImage.style.height=0
        this.$refs.play.style.display='block'
      }
      this.$refs.bgImage.style.zIndex=zIndex

      //向下开始滚动 图片放大效果
      this.$refs.bgImage.style['transform']=`scale(${scale})`
      this.$refs.bgImage.style['webkitTransform']=`scale(${scale})`
    }
  },
  created(){
    this.probeType=3,
    this.listenScroll=true
  },
  data() {
    return {
      scrollY:0
    }
  },
  mounted(){
    // 滚动偏移值为  bgImge的高度
    this.offHeight=this.$refs.bgImage.clientHeight
    //layer向上滚动的最大滚动距离
    this.minHeight=-this.offHeight+SAVE_TOP
    //初始歌曲list的位置  在bgimg下面
    this.$refs.list.$el.style.top=`${this.offHeight}px`
  },
  components:{
    scroll,
    songList,
    loading
  },
  props: {
    bgImage: {
      type:String,
      default:''
    },
    songs: {
      type:Array,
      default:[]
    },
    title: {
      type:String,
      default:''
    },
    rank: {
      type: Boolean,
      default: false
    }
  },
  computed: {
    bgStyle(){
      return `background-image:url(${this.bgImage})`
    }
  },

}
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  @import "~common/stylus/mixin"

  .music-list
    position: fixed
    z-index: 100
    top: 0
    left: 0
    bottom: 0
    right: 0
    background: $color-background
    .back
      position absolute
      top: 0
      left: 6px
      z-index: 50
      .icon-back
        display: block
        padding: 10px
        font-size: $font-size-large-x
        color: $color-theme
    .title
      position: absolute
      top: 0
      left: 10%
      z-index: 40
      width: 80%
      no-wrap()
      text-align: center
      line-height: 40px
      font-size: $font-size-large
      color: $color-text
    .bg-image
      position: relative
      width: 100%
      height: 0
      padding-top: 70%
      transform-origin: top
      background-size: cover
      .play-wrapper
        position: absolute
        bottom: 20px
        z-index: 50
        width: 100%
        .play
          box-sizing: border-box
          width: 135px
          padding: 7px 0
          margin: 0 auto
          text-align: center
          border: 1px solid $color-theme
          color: $color-theme
          border-radius: 100px
          font-size: 0
          .icon-play
            display: inline-block
            vertical-align: middle
            margin-right: 6px
            font-size: $font-size-medium-x
          .text
            display: inline-block
            vertical-align: middle
            font-size: $font-size-small
      .filter
        position: absolute
        top: 0
        left: 0
        width: 100%
        height: 100%
        background: rgba(7, 17, 27, 0.4)
    .bg-layer
      position: relative
      height: 100%
      background: $color-background
    .list
      position: fixed
      top: 0
      bottom: 0
      width: 100%
      background: $color-background
      .song-list-wrapper
        padding: 20px 30px
      .loading-container
        position: absolute
        width: 100%
        top: 50%
        transform: translateY(-50%)
</style>